A PDP displays pictures with a gas discharge causing ultraviolet rays and exciting phosphor with the ultraviolet rays.
The PDP is roughly classified into an AC type and a DC type for its driving method, and a surface discharge type and an opposing discharge type for its discharge scheme. Presently, the AC and surface discharge type with three electrodes makes a mainstream of the PDP because of its convenience for producing a high-precision and large screen, and of its simplicity in manufacturing. The AC and surface discharge type PDP is composed of a front panel and a back panel. The front panel has, on its substrate such as of glass, display electrodes each composed of a scanning electrode and a sustain electrode, a dielectric layer covering the electrode, and a protective layer covering the dielectric layer. The back panel has a plurality of address electrodes, a dielectric layer covering the address electrodes, barrier ribs formed on the dielectric layer, and phosphor layers formed on the dielectric layer and sides of the barrier ribs. The front panel and the back panel are oppositely faced so as the display electrodes and the address electrodes cross each other at a right angle forming a discharge cell between the display electrode and the address electrode.
This type of PDP features a higher display speed, a wider view angle, easier production of a large screen and a higher display quality by its self-luminescence, compared to a liquid crystal panel. Because of the features, the PDP is getting a particular attention in flat panel displays and is used for various applications as a display device for public places and as a display device at home for enjoying a large screen picture at home.
In above constitution of the PDP, the protective layer and the display layer of the front panel and the data electrode of the back panel are produced by a film forming method by vaporizing or sputtering for instance, and which example is disclosed in ‘2001 All about FPD Technology’ (Oct. 25, 2000) issued by Electronic Journal Inc., (pp 576 to 580).
When the film is formed on a substrate of the front panel or of the back panel as described, in order to form the film successively on the substrate, the substrate is sustained by a substrate holder and is conveyed by a conveyor composed of a transfer roller, a wire and a chain by touching or connected with the holder. Because the conveying method is as such, size of the substrate holder is much larger than the substrate. Consequently the film is formed on an exposed zone of the conveyor other than the substrate and stuck there. As the film is stacked on the exposed over and over, a part of the stuck film is chipped off becoming a source of dust in the film forming apparatus. Dust in the apparatus is caught by the film on the substrate or mixed with film forming material and badly affect quality and uniformity of the film on the substrate.
In order to solve above problem, the film which is stuck to the substrate holder has to be removed regularly before it becomes thick enough to be chipped off. However, because the PDP has a large screen size of 42 inches or 50 inches, the substrate is correspondingly heavy and the substrate holder must be strong and heavy enough to stably hold and transport the large and heavy substrate. Removing the stuck film from the substrate holder is therefore a very heavy labor, and operation is difficult and inefficient. In addition to it, the substrate holder must be taken out for removing the film during film forming process, stopping the process and dropping production efficiency.
The present invention is to overcome the problems, and aims to prevent dust to be formed in the film forming apparatus, which badly affects quality of the film when it is formed on the substrate of the PDP, and achieve a good picture quality of the PDP.